Physiologic Changes in Pregnancy and Their Impact on Diagnosis and Treatment

• Physiologic changes in pregnancy:
  • A detailed knowledge of the normal physiologic changes in pregnancy is crucial for managing critically ill pregnant patients.
  • These changes can complicate diagnosis and treatment in pregnant patients with additional pathology.
  • Physiologic changes during pregnancy alter the presentation of diseases and can unmask previously silent diseases.
  • Treatment endpoints can be different in pregnant patients compared to nonpregnant patients.
• Cardiovascular changes in pregnancy:
  • Cardiac output is significantly increased during pregnancy, primarily due to an increase in stroke volume.
  • Venous return is compromised by changes in body position, especially when the pregnant patient is supine.
  • Maternal body position influences hemodynamic alterations occurring in pregnancy.
  • Left lateral position is optimal to maintain venous return and cardiac output in pregnancy.
  • Cardiac compressions can be performed with manual displacement of the uterus or using alternative positions.
• Oxygen consumption and ventricular performance:
  • Maternal oxygen consumption increases during pregnancy, mostly due to the metabolic needs of the fetus.
  • Cardiac output increases before the rise in maternal oxygen consumption.
  • Echocardiographic studies show improved ventricular dynamics during pregnancy.
  • Hemodynamic changes during labor and delivery are influenced by anesthetic and analgesic techniques.
• Hemodynamic changes during labor and delivery:
  • Cardiac output significantly increases during active labor and immediately after delivery.
  • Uterine contractions can cause a rise in cardiac output and stroke volume.
  • The supine position accentuates the hemodynamic changes during labor and delivery.
• Cardiac Output:
  • Cardiac output increases during pregnancy, with a greater increase after delivery.
  • Blood volume changes contribute to the increase in cardiac output.
• Blood Volume Changes:
  • Maternal blood volume increases significantly during pregnancy, with plasma volume increasing by 30%-50%.
  • Blood volume is maximal at 30-34 weeks of gestation.
  • Both sodium and water retention contribute to the increase in plasma volume.
• Physiologic Anemia of Pregnancy:
  • An increase in RBC mass occurs during pregnancy, but it is disproportionate to the increase in blood volume.
  • Hematocrit levels decrease during pregnancy, resulting in a physiologic hemodilutional anemia.
  • Iron supplementation is important to prevent iron-deficiency anemia.
• Renal Adaptations:
  • Renal blood flow increases during pregnancy, with the glomerular filtration rate increasing by 50%.
  • Renal blood flow plateaus early in pregnancy and remains unchanged or slightly decreases as term approaches.
  • Glycosuria and urinary stasis can occur during pregnancy.
• Blood Pressure Changes:
  • Blood pressure usually decreases in the second trimester and then gradually increases towards term.
  • Peripheral vascular resistance decreases during pregnancy.
  • Blood pressure may increase during labor and delivery.
• Vascular System:
  • Hormonal changes and vascular remodeling contribute to decreased arteriolar tone and increased venous compliance.
  • Pregnancy is associated with a hypercoagulable state, increasing the risk of venous thrombosis.
• Hypovolemia and Hemorrhage:
  • The increased plasma volume associated with pregnancy can mask signs of hypovolemia.
  • A pregnant woman can lose up to 35% of her blood volume before showing signs of acute hemorrhage.
• Fluid Resuscitation:
  • Aggressive fluid resuscitation is the treatment of choice for severe hypotension during pregnancy.
  • Vasopressors may be necessary if hypotension is refractory to fluids.
• Vasopressors and Uterine Blood Flow:
  • Vasopressors increase maternal blood pressure and vasoconstriction of uterine vessels, but ephedrine and dopamine can increase uterine blood flow.
  • Limited human studies on the effects of vasopressors in pregnant women, but animal studies suggest potential benefits.
• Structural Changes in the Heart:
  • During pregnancy, the heart undergoes dramatic remodeling with enlargement of all four chambers and increased left ventricular mass.
  • Chamber enlargement, particularly of the left atrium, may be a predisposing factor for supraventricular and atrial arrhythmias.
• Cardiac Symptoms and Murmurs:
  • Pregnant women may experience symptoms such as fatigue, decreased exercise tolerance, palpitations, and chest pain.
  • New murmurs, including systolic flow murmurs and a third heart sound, are common in pregnancy.
• Cardiac Disease and Pregnancy:
  • Women with significant cardiac pathology are at risk during pregnancy, with increased maternal and fetal morbidity and mortality.
  • Maternal mortality is less than 1% for patients with less severe cardiac problems, but increases for high-risk patients.
• Endocrine and Metabolic Changes in Pregnancy:
  • Pregnancy leads to numerous endocrine and metabolic alterations, influenced by hormonal signals from the fetoplacental unit.
  • Endocrine and metabolic disorders may present with symptoms similar to the hypermetabolic state of pregnancy.
• Hypothalamic and Pituitary Alterations:
  • Hypothalamic–pituitary axis changes during pregnancy, with increased production of releasing hormones by the placenta.
  • Pituitary gland enlarges and shows changes in hormone production, such as increased synthesis of ACTH, prolactin, and TSH.
• Cortisol and Prolactin Levels:
  • Cortisol levels increase in pregnancy, blunting the normal negative feedback loop between ACTH and cortisol concentrations.
  • Prolactin levels increase significantly during pregnancy and may lead to the enlargement of preexisting pituitary adenomas.